The future with lower carbon concrete

When it comes to greenhouse gas emissions, it’s easy to focus on coal-fired power plants and internal combustion engines. They produce plenty of carbon dioxide, but another major source is less well known: the manufacture of cement and concrete.

“The cement manufacturers are the second largest emitters of CO2 in the world,” says Tom Schuler, who is president and CEO of Solidia Technologies ® in Piscataway, New Jersey. “They produce 5 to 7 per cent of all the CO2 that’s emitted.”

That is partly due to the sheer scale of the industry, says Schuler. “Concrete is the most used material on the planet after water.” And the chemical processes involved in making cement and concrete have always emitted carbon dioxide. Now Solidia has a way to rein that in.

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Cement is essentially made of calcium and silica, generally in the form of limestone and sand respectively. Cement manufacturers mix two parts limestone and one part sand, then heat the mixture in a kiln at 1500°C, transforming it into cement. The method has barely changed since the 1840s, when Joseph Aspdin and his son William developed and patented Portland cement.

This process produces carbon dioxide in two ways. The first is in heating the kiln, usually through burning fossil fuels. The second is the ensuing chemical reaction, which breaks down the limestone and liberates CO2.

Solidia has a new approach that releases far less carbon dioxide. It uses the same raw materials in a 50:50 blend, heated to a lower temperature of about 1200°C. This cuts both sources of carbon dioxide: it uses less limestone and less fossil fuel.

There is another advantage, too. Cement is usually mixed with sand, water and aggregate – rock fragments – to make concrete for construction. The water reacts with the cement, causing it to harden in a process called curing.

Solidia cement cures in a different way: by reacting with carbon dioxide that is pumped in. “You’ll actually see the [concrete] pick up about 5 per cent weight and that’s the CO2 converting to, essentially, limestone,” says Schuler.

This is part of a small but growing effort to capture and use carbon emissions. To that end, Solidia wants to locate its plants wherever carbon dioxide is readily available. “It may be more cost-effective to put a concrete plant next to a source,” says Schuler. An obvious source would be an oil refinery. “We think we can handle just about any gas that’s coming out of flues.” That’s one reason BP has invested in Solidia Technologies and included the firm in its Advancing Low Carbon programme that is helping to drive low carbon thinking across the company .

For now, Solidia is focused on getting its cement and concrete used by major manufacturers. To encourage uptake, the Solidia process is designed to be as similar as possible to existing practice so that manufacturers can use their existing equipment and raw materials.

Ultimately, Solidia wants to be part of the solution to climate change. “Our goal is to turn CO2 from a problem into a solution,” says Schuler.